The overall goal of this proposal is to elucidate the physiological and cellular mechanisms responsible for the regression of the primate corpus luteum as well as to understand the mechanisms by which the lifespan of the corpus luteum is prolonged during early pregnancy. Results of our previous work have identified two dramatic alterations that occur in luteal cells following ovulation: i) a cessation of the expression of the cAMP and PKA- dependent nuclear transcription factor CREB and ii) a dramatic decrease in the responsiveness of the corpus luteum to LH that occurs during the mid through late luteal phase of the menstrual cycle that is ultimately responsible for luteal regression. The goal of the research presented in the current proposal is to directly test the hypothesis that the eruption in intracellular cAMP levels that occurs in response to the mid-cycle gonadotropin surge sets into play a program of intracellular effectors that result in diminishing trophic effects of LH and this is regulated by the down-regulation of the cAMP-dependent nuclear transcription factor CREB. This hypothesis will be tested using state of the art physiological and molecular approaches. Aim 1 will identify the cellular mechanisms responsible for the loss of CREB expression during luteinization. The specific hypothesis is that the large increase in ovulatory cAMP levels directs the expression of the CREB transcription repressor ICER and this is temporally associated with the cessation of CREB and PCNA expression. In Aim 2, a recombinant adenovirus vector that expresses a dominant-negative mutant of CREB will be used to block CREB signaling in granulosa cells. The specific hypothesis is that the loss of CREB- of CREB and PCNA expression. In Aim 2, a recombinant adenovirus vector that expresses a dominant-negative mutant of CREB will be used to block CREB signaling in granulosa cells. The specific hypothesis is that the loss of CREB-mediated transcription will directly inhibit PCNA expression and cell proliferation but will not inhibit the acute effects of LH on progesterone production. Aim 3 will use adenoviral vectors in vivo in monkeys to constitutively activate the cAMP/PKA/CREB signaling pathway. The specific hypothesis is that activation of this signaling system will bypass the decline in LH receptors and prolong the functional lifespan of the primate corpus luteum. In addition to providing novel information regarding the physiology of the primate corpus luteum, results of these studies will further our understanding of the causes of luteal phase defects in humans which are thought to be a significant cause of infertility and early pregnancy loss. Further, our novel use of adenoviruses to directly alter ovarian protein expression in vivo will provide new ways to approach the understanding of other ovarian disorders that impact upon women's health such as polycystic ovarian disease.